The finding of the position of a geophysical research vessel must be highly accurate so as to ensure proper correlation between anomalies observed in the earth's crust on the one hand and the available data on the earth's crust in the area under investigation and cartographic depth information on the other hand. In the case of shelf exploration, the permissible position finding error must not be in excess of a few meters, otherwise subsequent prospecting drilling will only result in a loss of time and money. However, the existing systems for graphic representation of a vessel's position on the map are such that, even with an accurate course and speed determination, the position finding error amounts to as high as 1 to 1.5 percent of the distance covered by the vessel. The error is too big, of course, and is largely due to errors involved in the automatic scale conversion of coordinates from the Descartes system, in which the longitudinal and latitudinal speed components are determined, to the Mercator map projection.